Method and apparatus for tracking maximum power point for inverters, for example, in photovoltaic applications

Abstract

A power system employs an outer voltage feedback loop and an inner current feedback loop to control a power converter, such as a DC to AC inverter for transferring electrical power between a power source, for example a photovoltaic array, and a load, for example a power grid. The outer loop accommodates variations in the output of the power source, for example accommodating anomalies in IV characteristics such as IV droop characteristic associated with photovoltaic cells. The outer loop may employ a first control regime or a second control regime, for example, dependent on whether a DC bus voltage or power is smaller than a value corresponding to measurement resolution or expected noise.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This disclosure is generally related to power inverters, and particularly to inverters that invert power from photovoltaic sources.[0003]2. Description of the Related Art[0004]A photovoltaic cell is one of the cleanest and environment-friendly non-conventional energy sources. A photovoltaic cell directly converts solar energy into electrical energy. The electrical energy produced by the photovoltaic cell can be extracted over time and used in the form of electric power. This electric power can be used to drive electric devices. Typically the power is extracted by use of DC-DC up / down converter circuitry and / or DC / AC inverter circuitry.[0005]The popularity of photovoltaic energy generation is rapidly increasing worldwide. One reason for such popularity is that the energy produced by photovoltaic energy generation is essentially pollution free, unlike conventional energy sources such as fossil fuel burning thermal power p...

AI Technical Summary

Benefits of technology

"The patent describes a method for controlling a power system that includes a photovoltaic source and an inverter. The method involves determining a DC voltage reference value based on the characteristics of the photovoltaic source, and a current reference value based on the difference between the determined DC voltage reference value and the voltage across the DC bus. The method then produces control signals for the inverter based on the current reference value. The method can adjust the DC voltage reference value based on changes in power produced by the photovoltaic source and can determine the current reference value based on the difference between the DC voltage reference value and the voltage across the DC bus. The method can also combine two control regimes to increase or decrease the DC voltage reference value based on changes in power produced by the photovoltaic source. The technical effect of the patent is to provide a more efficient and effective method for controlling a power system that includes a photovoltaic source and an inverter."

Problems solved by technology

However, there are difficulties encountered with photovoltaic energy generation which are not present in conventional energy generation systems.

These issues include the peculiar IV droop characteristics of photovoltaic cells, the cost, and the relatively low energy density (efficiency) of photovoltaic cells.

Photovoltaic cells are still relatively expensive and it's energy conversion efficiency is still relatively low so a wide area is required to generate sizable power.

Although this technique attempts to track the MPP without explicitly computing the voltage-current product for the panel power, the curve-fitting technique cannot predict many characteristics including other complex factors, such as aging, temperature, and a possible breakdown of individual cells.

This requires a very slow filter in the power calculation and voltage measurements which may detrimentally limit the response time.

Thus, a rapid change in isolation level may cause problems in systems employing such techniques.

Consequently, such an approach is not cost effective.

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